1. Field of the Invention
The present invention relates to an active matrix type liquid display system such as a display unit used in a personal computer.
2. Description of the Related Art
The conventional active matrix type crystal display system has used transparent electrodes formed on the interfaces between the liquid crystal and two substrates facing to each other as electrodes driving a liquid crystal layer. The cause is that the conventional active matrix type crystal display system has employed a twisted nematic display type in which.liquid crystal is driven by directing the electric field applied to the liquid crystal in the direction approximately perpendicular to the interfaces.
On the other hand, an active matrix type liquid crystal display system has been proposed in Japanese Patent Application Laid-Open No. 56-91277 (1981) in which liquid crystal is driven by directing the electric field applied to the liquid crystal in the direction approximately parallel to the interfaces.
In the conventional technology employing the twisted nematic display type described above, it is required to form a transparent electrode such as indium tin oxide (ITO) typical. However, since the transparent electrode has an unevenness of approximately several ten nm on its surface, it becomes difficult to fabricate a fine active element such as thin film transistor (hereinafter referred to as xe2x80x9cTFTxe2x80x9d). Further, since the projected part of the transparent electrode is often apt to be detached and mixed into other parts such as electrode, the yield of the products has been largely decreased.
Furthermore, there have been a lot of problems on the aspect of image quality in the conventional technology. Especially, it has been difficult to obtain a halftone display since change in brightness is large when the view direction is changed.
Still further, in the active matrix type liquid crystal display system using switching transistor elements, it is required to provide a.scanning electrode and a signal electrode for driving the switching transistor elements in addition to a pixel electrode for applying voltage or electric field to liquid crystal to modulate transmitted light or reflected light. The scanning electrode and the signal electrode fluctuate the voltage in the pixel electrode through the parasitic capacitance Cgs between the scanning electrode and the pixel electrode and the parasitic capacitance Cds between the signal electrode and the pixel electrode. In particular, since the voltage in the signal electrode is always fluctuated by image information, the voltage in the pixel electrode is fluctuated through the parasitic capacitance Cds between the signal electrode and the pixel electrode to decrease the contrast or to produce a bad image called as cross-talk.
In the type in which the electric field applied to the liquid crystal in the direction approximately parallel to the interfaces of the substrates, there has been problem that the parasitic capacitance Cds between the signal electrode and the pixel electrode becomes large comparing to the case of the twisted nematic display type, the cross-talk being large, the contrast being decreased depending on the image pattern. The cause is that since a common electrode in the type applying the electric field to the liquid crystal in the direction approximately parallel to the interfaces of the substrates is not formed over the whole surface of the substrate facing against the substrate having switching transistor elements different from in the case of the twisted nematic display type, the line of electric force from the signal electrode is not shielded and is terminated at the pixel electrode. Therefore, in the type applying the electric field to the liquid crystal in the direction approximately parallel to the interfaces of the substrates, the active matrix driving has a disadvantage in image quality.
The first object of the present invention is to provide an active matrix liquid crystal display system which requires no transparent electrode.
The second object of the present invention is to provide an active matrix liquid crystal display system which is good in view angle characteristic and easy in multi-halftone display.
The third object of the present invention is to provide an active matrix liquid crystal display system which is high in contrast and high in quality of image without cross-talk.
The structure of the active matrix liquid crystal display system according to the present invention to attain the above objects is as follows:
(1) A liquid crystal composition is interposed between a first and a second substrates, a plurality of pixel parts being constructed with a plurality of scanning electrodes and a plurality of signal electrodes arranged in a matrix, switching element being provided in each of the pixel parts. The switching element is connected to the pixel electrode, and the pixel electrode and the common electrode facing against the pixel electrode are so constructed as to be operable in keeping the major axes of the liquid crystal molecules parallel to the surface of the substrate.
In the pixel part, the signal electrode and the pixel electrode are formed, and a shield electrode is formed between the signal electrode and the pixel electrode.
(2) According to another feature of the present invention, the shield electrode is formed in a light transmitting part except the light transmitting part between the pixel electrode and the common electrode.
(3) According to a further feature of the present invention, a light shield film being black or having a low light transmittance containing a pigment or dye is formed in the light transmitting part except the light transmitting part between the pixel electrode and the common electrode.
(4) According to a still further feature of the present switching element is connected to the pixel in the pixel part, the signal electrode is invention, the electrode, and formed, and the shield electrode is formed between the signal electrode and the pixel electrode.
The shield electrode and the pixel electrode are formed and are so constructed as to be major axes of the liquid crystal in facing to each other, operable in keeping the molecules parallel to the surface of the substrate.
(5) According to a further feature of the present invention, a part of the shield electrode is so formed as to overlap with the signal electrode.
(6) According to a further feature of the present invention, a light shield film being black or having a low light transmittance containing a pigment or dye is formed in the light transmitting part except the light transmitting part between the pixel electrode and the shield electrode.
(7) According to a still further feature of the present invention, the shield electrode is formed on the first substrate.
(8) According to a still further feature of the present invention, the shield electrode is formed on the same layer as the signal electrode is formed.
(9) According to a still further feature of the present invention, the shield electrode is formed on the same layer as the scanning electrode is formed.
(10) According to a still further feature of the present invention, the switching element is a thin film transistor having a positive stagger structure.
(11) According to a still further feature of the present invention, the shield electrode is projected from a scanning wire toward the longitudinal direction of a signal wire.